all: use lower-case letters at the start of error message

Signed-off-by: Josh Bleecher Snyder <josharian@gmail.com>

cmd/tailscaled/tailscaled_windows.go

@@ -168,7 +168,7 @@ func startIPNServer(ctx context.Context, logid string) error {
 		r, err := router.New(logf, dev)
 		if err != nil {
 			dev.Close()
-			return nil, fmt.Errorf("Router: %w", err)
+			return nil, fmt.Errorf("router: %w", err)
 		}
 		if wrapNetstack {
 			r = netstack.NewSubnetRouterWrapper(r)
@@ -188,7 +188,7 @@ func startIPNServer(ctx context.Context, logid string) error {
 		if err != nil {
 			r.Close()
 			dev.Close()
-			return nil, fmt.Errorf("Engine: %w", err)
+			return nil, fmt.Errorf("engine: %w", err)
 		}
 		onlySubnets := true
 		if wrapNetstack {

wgengine/router/ifconfig_windows.go

@@ -359,7 +359,7 @@ func configureInterface(cfg *Config, tun *tun.NativeTun) (retErr error) {
 			firstGateway6 = &ipnet.IP
 		} else if route.IP.Is4() && firstGateway4 == nil {
 			// TODO: do same dummy behavior as v6?
-			return errors.New("Due to a Windows limitation, one cannot have interface routes without an interface address")
+			return errors.New("due to a Windows limitation, one cannot have interface routes without an interface address")
 		}
 
 		ipn := route.IPNet()